I. Technical Field
This invention pertains to telecommunications, and particularly prioritization of communications on an uplink from plural wireless terminals to a radio access network node.
II. Related Art and Other Considerations
In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability), e.g., mobile termination), and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions (particularly earlier versions) of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base stations nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
The evolved UTRAN (E-UTRAN) comprises evolved base station nodes, e.g., evolved NodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the user equipment unit (UE). The eNB hosts the following functions (among other functions not listed): (1) functions for radio resource management (e.g., radio bearer control, radio admission control), connection mobility control, dynamic resource allocation (scheduling); (2) mobility management entity (MME) including, e.g., distribution of paging message to the eNBs; and (3) User Plane Entity (UPE), including IP Header Compression and encryption of user data streams; termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. The eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. The eNodeB also offers Radio Resource Control (RRC) functionality corresponding to the control plane. The eNodeB performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers.
The Layer 3 (L3) of the LTE radio access network (RAN) contains the Radio Resource Control (RRC) functionality of the radio network. Examples of RRC functionality are RRC connection setup, bearer setup, and handover procedures and configuration of measurements. The L3 control signaling carries information between the RRC layer in RAN and the corresponding layer in the wireless terminals (e.g., UEs), and is carried over so-called Signaling Radio Bearers (SRB) on the Physical Uplink Shared Channel (PUSCH) and Physical Downlink Shared Channels (PDSCH). The user plane data is carried on ordinary Radio Bearers (RB), which is also mapped to the PUSCH and PDSCH.
The performance of L3 control signaling, in terms of delay, directly impacts the quality of service (QoS) of the user plane data transmission. Since the L3 signaling and the user plane data are carried on the same physical channels (the PUSCH and PDSCH), the Signaling Radio Bearers (SRBs) need to be prioritized relative to other radio bearers. The allocation of PDSCH and PUSCH, to different radio bearers and Signaling Radio Bearers (SRBs), is administrated by a scheduler(s) which is/are situated in the eNodeB. A task of a the scheduler is to prioritize different transmissions from different wireless terminals and to allocate the resources (including the uplink resources) efficiently.
There are three types of Signaling Radio Bearers (SRBs). A first type of Signaling Radio Bearer (SRB) is SRB0, which is carried in CCCH. A second type of Signaling Radio Bearer (SRB) is SRB1, for NAS messages and for most RRC messages, all using DCCH logical channel. A third type of Signaling Radio Bearer (SRB) is SRB2, which is for high-priority RRC messages, using DCCH logical channel. The differences between these types of Signaling Radio Bearers (SRB) are described in 3GPP TS 25.331 V8.1.0 (2007-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 8).
In downlink, prioritization of resources between wireless terminals is easy to achieve since the network controls and knows the type of data that the network wants to transmit to the different wireless terminals. However, in uplink, the network does not have information about the types of transmissions the wireless terminals want to send to the network until it receives a Buffer Status Report (BSR) from the wireless terminals. The Buffer Status Report (BSR) includes detailed information about the buffers of the wireless terminal from which the Buffer Status Report (BSR) is sent. In the Buffer Status Report (BSR), the size of the buffers per radio bearer (RB) group is reported (a radio bearer (RB) group is a group of similar radio bearers (RBs).
A Buffer Status Report (BSR) includes, among other things, information about the type of radio bearers (RBs) in the buffer of the wireless terminal, so that from the Buffer Status Report (BSR) the presence of a Signaling Radio Bearer (SRB) in the buffer can be discerned. If a Signaling Radio Bearer (SRB) is present in the Buffer Status Report (BSR) for a particular wireless terminal, the network can prioritize the corresponding wireless terminal.
However, in order to transmit a Buffer Status Report (BSR) from a wireless terminal to the network, an uplink grant from the network to the wireless terminal is required. Initially, the wireless terminal does not have any such uplink grant, and therefore the wireless terminal must send a special communication known as a Scheduling Request (SR) on the PUCCH to the network to apply for (e.g., request) resources for transmission of the Buffer Status Report (BSR). The Scheduling Request (SR) is only one bit in length. In view of the small size of the Scheduling Request (SR), no detailed information about the radio bearers (RB) in the buffer of the request wireless terminal can be obtained from the Scheduling Request (SR). So the Scheduling Request (SR) itself provides no basis for knowing buffer content or prioritizing communications. In other words, upon reception of a mere Scheduling Request (SR), the eNodeB cannot prioritize the Signaling Radio Bearer (SRB) over other Radio Bearers since it does not yet know of the Signaling Radio Bearer (SRB).
A current approach to the prioritization of Signaling Radio Bearers (SRBs) in the uplink is described FIG. 1. The approach is based on, e.g., involves, the Buffer Status Report (BSR). When the eNodeB receives a Scheduling Request (SR), the eNodeB sets the priority level to between the priority level of the Signaling Radio Bearer (SRB) and the normal data radio bearer (RB) priority level since the eNodeB does not know what data is in the buffers of the wireless terminal.
Ordinarily the scheduler of the eNodeB will choose which wireless terminal is allowed to transmit, with the wireless terminals being granted transmission rights in accordance with a decreasing priority level. In other words, the wireless terminal with the highest priority level is granted first transmission, the wireless terminal with the second highest priority level is granted second transmission, and so forth. If and when a wireless terminal is scheduled to transmit, the scheduler (together with the link adaptation function) issues a grant to the wireless terminal. The grant indicates the size of the coded transport block that the wireless terminal is allowed to transmit. The transport block generally includes the physical layer data unit which the wireless terminal wants to transmit over the air interface to the eNodeB, and can also include a Buffer Status Report (BSR). The grant is expressed in bytes, e.g., “x bytes”, which is a configurable parameter.
Since the scheduler does not know how much data is currently in the buffer of the wireless terminal, an attempt is made to make the grant size at least larger than the size of a Buffer Status Report (BSR). The size of the grant is typically selected from a fixed table of transport block sizes and should at least be the size of the Buffer Status Report (BSR).
In the wireless terminal the Buffer Status Report (BSR) has absolute highest priority for uplink transmission (in accordance with 3GPP Technical Specifications). Upon the reception of the grant, if the grant size is larger than the total buffer size of the wireless terminal plus the size of the Buffer Status Report (B SR), both user data and the Buffer Status Report (BSR) are transmitted by the wireless terminal. If the grant size is larger than the total buffer size but smaller than the size of the total buffer plus the size of the Buffer Status Report (BSR), the wireless terminal data (“UE data”) without the Buffer Status Report (BSR) is transmitted. If the grant size is larger than the size of the Buffer Status Report (BSR), but smaller than the total buffer size plus the size of the Buffer Status Report (BSR), the Buffer Status Report (BSR) plus part of the UE data will be transmitted. Since the Signaling Radio Bearer (SRB) has higher priority than normal traffic data (“UE data”), the wireless terminal will transmit the L3 message first. In other words, the L3 signaling is prioritized.
Several problems attend the existing approach of uplink prioritization. For example, the current approach does not solve the problem that eNodeB has no knowledge about buffer of the wireless terminal before the eNodeB receives a Buffer Status Report (BSR), so the same priority level is set both for wireless terminals having the important L3 signaling and wireless terminals having normal data. When resources are limited, the eNodeB may sacrifice or overlook the wireless terminal that actually has L3 signaling in its buffer.
Another problem with the current approach is that the buffer estimate x attributed to the buffer of a wireless terminal is assumed to be an arbitrary and fixed value. For the case when there is a small amount of data in the buffer of the wireless terminal, the buffer estimate x may be too large and therefore resources can be over allocated. On the other hand, for the case when there is more data in the buffer of the wireless terminal than x bytes, the data will be truncated to two messages and thus add more over head to the communications. An increased number of communications will result in insufficient resource usage, and possibly extra user plane delay. Moreover, as understood from the above, the wireless terminal sending both a Scheduling Request (SR) and a Buffer Status Report (BSR) can waste resources over the air interface and add a large delay before the corresponding L3 signaling is actually sent.